INTERACTION OF NITRIC-OXIDE AND CYCLIC GUANOSINE 3',5'-MONOPHOPHATE IN ERYTHROPOIETIN PRODUCTION

The present study was designed to investigate whether in vivo and in v itro erythropoietin (EPO) production is modulated by nitric oxide (NO) and cyclic guanosine 3',5'-monophosphate (cGMP). Serum levels of EPO in exhypoxic polycythemic mice were significantly increased after inje ctions of 200 mug / kg sodium nitroprusside for 4 d. One injection of N(G)-nitro-L-arginine methyl ester (L-NAME) produced a significant dos e-related decrease in serum levels of EPO in exhypoxic polycythemic mi ce in response to hypoxia. When EPO producing Hep3B cells were incubat ed in 1% 02 for 30 min, cGMP levels in the Hep3B cells were significan tly elevated, compared with cells incubated in 20% O2. The elevation o f cGMP by hypoxia was inhibited by L-NAME (100 muM). Sodium nitroprusi de (10 and 100 muM) and NO (2 muM) also significantly increased cGMP l evels in Hep3B cells. L-NAME, LY 83583 (6-Anilino-5,8-quinolinedione, a soluble guanylate cyclase inhibitor), and Rp-8-Bromo-cGMPS (Rp-8-Bro mo-guanosine 3',5'-cyclic monophosphothioate, a cGMP-dependent protein kinase inhibitor) significantly inhibited the hypoxia-induced increas e in medium levels of EPO in Hep3B cells. 8-Bromo-cGMPS produced a dos e-dependent decrease in EPO messenger RNA levels in Hep3B cells in res ponse to hypoxia. 8-Bromo-cGMP (10(-3) M) produced significant increas es in medium levels of EPO in Hep3B cell cultures incubated under norm oxic conditions, which was enhanced by the phosphodiesterase inhibitor , 3-isobutyl-1-methylxanthine (0.2 mM). These results suggest that NO and cGMP may interact in modulating hypoxic stimulation of EPO product ion.